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Abstract— Several surface coatings on Ti-6Al-4V alloy using
laser treatment technique have been investigated in this paper.
A hybrid Ti-6Al-4V based metal matrix composites system was
also successfully fabricated. This was possible using three hoper
system which contained 3.8 vol. % of Ti-6Al-4V and a small
amount 0.1 B4C and 0.1 BN respectively. Two different laser
powers “2000 W and 1400 W with scanning speed of 1.0 were
employed. The idea of these powder coatings and reason for
investigating the different Laser power is to evaluate the
influence of laser power on the surface morphology and
hardness property of Ti-6Al-4V/B4C/BN alloy systems. The
hardness result of experimental showed a general improvement.
The hardness revealed that the Ti-6Al-4V/B4C/BN system
fabricated at 2000W showed a hardness improvement as high
as 640.4 HVO.5 compared to the as receive Ti-6Al-4V substrate
Hardness value of about 357.3 HVO.5 and that of 1400W
recorded a hardness value of 886 HVO.5. The percentage
increase from the as received Ti-6Al-4V alloy was 147.9% and
79.2% respectively. Problems to be solved and the prospective
application of laser modification of the hybrid titanium alloy
formed were also highlighted.
Index Terms— Ti6Al4V Substrate alloy, Ti-6Al-4V, B4C and
BN powder. Laser Coating
I. INTRODUCTION
arious surface treatments have been used to improve
the mechanical properties of Ti-6Al-4V alloy. Surface
treatments such as laser nitriding and tin coated surface
treatment on Ti-6Al-4V alloy surfaces have been
investigated to further improve the mechanical properties of
Ti-6Al-4V alloy for effective applications. These techniques
have been demonstrated to form nitride rich compounds on
the surface region of materials to form a hard surface and
improve their tribological properties. A typical example is
the TiN PVD coated surface which has been proven to
reduce the surface roughness of material thus forming hard,
Mr Onyeka. F. Ochonogor is a Ph.D Student in the Department of
Mechanical Engineering Science, Faculty of Engineering and the Built
Environment, University of Johannesburg, Kingsway Campus Auckland
Park, Johannesburg, 2006. Phone: +27610564124; email:
Prof. Eseter. T. Akinlabi is in the Department of Mechanical
Engineering Science, Faculty of Engineering and the Built Environment
University of Johannesburg, Kingsway Campus Auckland Park,
Johannesburg, 2006. Phone: +27 11 559 2137; ([email protected]).
Dr. Kasongo D. Nyembwe is with the Department of Engineering
Metallurgy, Faculty of Engineering and the Built Environment,
Doornfontein Campus, University of Johannesburg 2986,
improved surface properties with increased elastic modulus
of the treated layer [1]. Fabrication of active films is
however needed on the surface of titanium alloys to further
improve compatibility often carried out by laser coating.
These processes potentially eliminate cracks and other
defects such as porosity and cavities.
Laser coating involving the use of Laser beam is focused
onto metallic surface to achieve a wide range of treatments
which includes remelting, alloying and cladding.
Thermal-barrier coatings like refractory-oxide ceramic
coatings applied to metallic surfaces may have application in
the hottest part of gas-turbine engines [2]. TBCs have
proven to provide thermal insulation to the metallic/super
alloy engine parts [3].
Titanium and its alloy exhibit attractive and interesting
properties, most importantly in terms of their mechanical
properties [4]. Despite the poor thermal conductivity and
accelerated tool wear during manufacturing of these special
alloys, they have shown potential for excellent application
both in aero engines and industrial gas turbine [5]. The
performance of titanium-based composite materials enables
its application for structural parts of rockets, aero engines,
and turbojet engines [6, 7]. However the application of this
alloy for Turbine engines/industrial turbines has remained a
challenge as the turbine temperature correlates to the
capacity and selected alloying material for reinforcement [8,
9]. In other to avoid problems such as defects, crack,
porosity which may lead to break down of system at high
temperature above 1000oC, a good thermal, fatigue resistant,
creep strength and high cycle fatigue material is however
needed since their operation requires a very high
temperature [10-12]. These properties can only be obtained
through intrinsic material resistance which is enhanced by
application of protective coatings on their surfaces. There
has been new technologies which has been used to modify
the surfaces of alloys with limiting factor of producing thin
surface layers, these technique includes; laser nitriding, laser
cladding, electron beam radiation processes e.t.c, their
limitations has been linked to costly manufacturing
procedures, vacuum chambers, and expensive initial
investments [21].
The fabrication of high thermal resistant material have
now evolved from the conventional casting to direct
solidification processes resulting to overall improvement in
mechanical properties. Various surface modification
technique including, effect of laser processing parameters on
the resultant surface properties of titanium alloys has also
Effect of Laser Power on the Microstructure and
Microhardness Property of Hybrid Fabricated
Ti6Al4V Based Metal Matrix Composite
Ochonogor O. Franklin, Esther T. Akinlabi, Member, IAENG, and Kasongo D. Nyembwe
V
Proceedings of the World Congress on Engineering 2016 Vol II WCE 2016, June 29 - July 1, 2016, London, U.K.
ISBN: 978-988-14048-0-0 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
WCE 2016
been reviewed in this paper.
II. CURRENT STATUS ON VARIOUS COATED TI-
6AL-4V ALLOY USING LASER TREATMENT
TECHNIQUES
Filip, 2008 [13] investigated laser nitriding surface layer
of Ti6Al4V alloy. The surface roughness and the Vickers
hardness under load of 1.96 N were carried out on the cross
sections of surface layer. The results however indicated that
the Laser remelting process produced a hard surface layer of
ceramics particles of TiN and Ti2N phases in martensitic
matrix. The hardness of surface layer also revealed a
significant increase compared to the untreated alloy which
was attributed to the formation of TiN and Ti2N particles.
The maximum hardness value of the laser treated surface
was about 1500 HV0.2. The wear resistance of laser nitrided
layer remarkably increased compared to the as received
material.
Kim et al., (2014) [15] carried out Laser Surface
Modification of Ti and TiC Coatings on Magnesium Alloy
in order to enhance its surface properties. The substrate
specimens were cut from a rolled sheet, and then the Ti and
TiC coatings were deposited on sand blasted untrasonic
cleaned AZ31 alloy substrates through air plasma thermal
spray. The TiC spray coating was carried out in situ reaction
between elemental Ti and carbon powders after ball mixing.
A combination of Ar and H2 was used as the plasma gas and
Ar was used as the powder carrier gas. The pre-deposited Ti
or TiC coatings on the specimens were then surface treated
using a continuous wave (CW) diode laser. The applied
power for the laser treatment was between 100 to 300 W,
and scanning speed was 14 mm/s. For oxidation to be
avoided during the process, an inert gas (Ar) was
continuously bellowed into the melting zone. Various
microstructural analysis were performed using SEM,
equipped with energy dispersive Xray spectrometer (EDS),
and Xray diffractometer (XRD). Surface melting process
application by plasma spraying of Ti or TiC on AZ31 alloy
revealed the formation of fine Ti particle dispersed surface
layer on the substrate. It was however reported that hardness
showed a significant improvement for the laser treated
specimens when compared to the untreated AZ31 alloy. In
the plasma sprayed specimen, there was an incomplete TiC
formation while the completely transformed TiC layer was
recorded after post laser melting process. Result also
revealed that the laser post treatment induced enhanced
adhesion strength between the coating and the substrate.
Filip et al., 2006 [16] attempted to study the effect of heat
treatment on microstructural properties as it influences the
strength of a material. The experiment involved two titanium
alloys which were (i) Ti-6Al-4V, and (ii) Ti-6Al-2Mo-2Cr.
It was however observed that the heat treatment resulted to a
wide variation in properties. The properties like yield stress,
tensile stress and ductility were remarkably improved
through a bimodal microstructure, as the region having
lamellar microstructure was characterized to have a
combined high fracture toughness and high fatigue crack
propagation resistance.
In a recent experiment involving the mixture of Zirconium
powder with PVA and cold glue as binder. These coatings
were used as reinforcement to improve the surface properties
of Ti-6Al-4V alloy [16]. A laser cladding experiment carried
out by irradiating the pre-placed powder bed at 500 W laser
power, 10mm/s Scan speed and of 1 mm beam spot size.
Powder mixture was melted to form a thin layer that is
bonded to the Ti6Al4V substrate by a method known as
irradiation to form a zirconium + zirconia composite due to
in-situ reaction observed in the liquid state. The observed
microstructure revealed some small pores and cracks. At
lower magnification, coatings were dense and crack-free,
and non-porous microstructures were achieved. It was
however reported that the presence of binder in the Zr
powder revealed a change in microstructure and resulted to a
significant increase in the hardness of the coated Ti6Al4V
alloy from the Cladded layer down to substrate of the
sample. It was also observed that Zr + PVA binder coating
was deposited uniformly with lesser dendritic structure in
comparison to Zr without binder and Zr with cold glue.
Manufactured Ti6Al4V alloy coatings with zirconium and
zirconia composite were however observed to have
improved the corrosion and wear resistance as reported.
III. EXPERIMENTAL PROCEDURE
A hybrid Ti-6Al-4V/ B4C/BN system was fabricated at
two different Laser power. 2000W and 1400W respectively.
The Scanning speed was kept constant at 1.0 and powder
flow rate of 3.8 Vol. % of Ti-6Al-4V, 0.1 Vol. of B4C and
0.1 Vol. BN. The effect of Laser power was investigated as
it influenced the microstructure, surface roughness and
hardness of the two hybrid systems formed. TABLE I
PROCESSING PARAMETERS
Sample Laser
power
Scanning
Speed
Powder
flow
rate
(Ti64)
Powder
flow rate
(B4C)
Powder
flow rate
(BN)
1 2000 1.0 3.8 0.1 0.1
2 1400 1.0 3.8 0.1 0.1
TABLE II
PROCESSING PARAMETERS AND AVERAGE HARDNESS VALUE
OF FABRICATED COMPOSITE. Sample Laser
power
Scan
Speed
Ti
Powder
flow
rate
B4C
Powder
flow
rate
BN
Powder
flow
rate
HVO.5
1 2000 1.0 3.8 0.1 0.1 640.4
2 1400 1.0 3.8 0.1 0.1 886
IV. RESULTS AND DISCUSSION
Fig. 1 Presents an optical micrographs of formation of
microstructures of titanium matrix composites obtained at
2000W with combined particle distribution of Ti-6Al-4V/
B4C/BN, the microstructure revealed more melted
reinforcement particles with lesser particle distribution
compared to the coating carried out at 1400W. A few pores
were evident as observed in Fig. 1 (a) and Fig. 1 (b)
respectively.
Proceedings of the World Congress on Engineering 2016 Vol II WCE 2016, June 29 - July 1, 2016, London, U.K.
ISBN: 978-988-14048-0-0 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
WCE 2016
Fig. 1. (a) 2000W, 3.8 Ti-6Al-4V+0.1 B4C+0.1BN
Fig. 1 (b) 2000W, 3.8 Ti-6Al-4V+0.1 B4C+0.1BN
Fig. 2. (a )1400 W, 3.8 Ti-6Al-4V+0.1 B4C+0.1BN
Fig. 2 (a) revealed that the bonding strength between the
surface clad layer and the substrate was very high and
homogeneous. This was also shown in Fig. 2 (b) Acicular
martensite was formed at the Heat affected Zone (HAZ) [20]
and a more uniform distribution of reinforcement particles
was also observed.
Fig. 2. (b) 1400 W, 3.8 Ti-6Al-4V+0.1 B4C+0.1BN
Fig. 2. (c) 1400 W, 3.8 Ti-6Al-4V+0.1 B4C+0.1BN
Fig. 2 (c) shows clear martensite in the niddle like
manner. This formation of hard microconstituent has been
found to be a determining factor for the high hardness
deduced from the hardness profile in fig. 3. The formation of
martensite in the case was due to the rapid cooling to room
temperature [19].
0 2 4 6 8 10 12
300
400
500
600
700
800
900
vic
kers
Ha
rdn
ess (
HV
N)
Identations
Cladded to Substrate
2000 W, 3.8Ti/B4C/BN
1400 W, 3.8 Ti/B4C/BN
Fig. 3. Hardness value of Ti-6Al-4V+ 0.1 B4C+ 0.1BN at
Proceedings of the World Congress on Engineering 2016 Vol II WCE 2016, June 29 - July 1, 2016, London, U.K.
ISBN: 978-988-14048-0-0 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
WCE 2016
different fabricated temperature.
The hardness profile at lower laser power revealed a
general increase in the hardness value of the coated area. A
sharp increase in hardness value before reduction as it
progresses towards the substrate, at the forth point of
indentation could be attributed to the unmelted solid carbide
particle embedded in the matrix as represented above. The
second profile represented with black dotted line also
showed a general increase in the hardness value though
lesser in Hardness value which could be attributed to a more
melted and weakened carbide particle due to high laser
power. See table II above.
V. CONCLUSION
In conclusion, Laser cladded Ti-6Al-4V/B4C/BN was
successfully fabricated.
The influence of laser power on the surface morphology,
hardness property has been investigated. The bonding
strength and particle distribution of the fabrication at 1400W
was excellent. This will enable thermal protection as
required for the development of laser surface modified
titanium alloy in the aerospace industry. It therefore suggests
that the fabricated component could have application in high
temperature condition i.e. in turbine parts.
ACKNOWLEDGMENT
The financial support of the global excellence and stature
(GES), University of Johannesburg is acknowledged.
REFERENCES
[1] A .Omar, A. Al-Mana, “Laser Nitrided and TiN Coated Ti-6Al-4V
Alloy Surfaces,” School of Mechanical & Manufacturing
Engineering. Dublin City University. 2011.
[2] R. C., David, O. Matthias & P. P. Nitin, “Failure Mechanisms of
Thermal Barrier Coatings for High Temperature Gas Turbine
Components under Cyclic Thermal Loading” 2012.
[3] R. C, David, O. Matthias, & P. P. Nitin, “Thermal-barrier coatings
for more efficient gas-turbine engines. Mrs. Bulletin. Vol. 37 No. 10.
2012 Pp. 873–976. www.mrs.org/bulletin.
[4] C. N., Elias, J.H.C., Lima, R. Valiev, & M.A. Meyers, “Biomedical
Applications of Titanium and its Alloys”. JOM.
www.tms.org/jom.html. 2008
[5] E. O. Ezugwu, & Z. M. Wang, “Titanium alloys and their
machinability”: a review. Journal of Materials Processing Technology
68. 1997, Pp. 262-274. Available at elsevier.com.
[6] K. A., Dinesh, S., Sathyanarayanan, D. G. Sayantan, & R.
Nageswara, “Gas Turbine Materials-Current status and its
Developmental Prospects-A Critical Review”, 2007.
[7] W. Karen, “Ceramic-matrix composites heat up”. High-Performance
Composites. 2013.
[8] R. M. Nageswara, “Materials for Gas Turbines – An Overview”. VIT
University India. Advances in Gas Turbine Technology. 2011, Pp.
293-314. Available at www.intechopen.com.
[9] P. B, Meherwan, “Gas Turbine Engineering Handbook”., Second
Edition, 2002.
[10] E. F., Campo, S.P.A., Avio, I., Torino, V. Lupinc, & B. I. Cinisello,
“High temperature structural materials for gas turbine”. (vol.11 (1).
1993.
[11] P. Vuoristo, J. Tuominen, & J. Nurminen, “Laser coating and thermal
spraying - process basics and coating Properties”. Tamper University
of Technology, Institute of Materials Science, Tampere /
FICentralOstrobotnian Technology Centre KETEK, Kokkola / FI.
2006
[12] L. Pawlowski, “Thick Laser Coatings: A Review”. ÓASM
International. JTTEE5 vol. 8: 1999, Pp. 279-295.
[13] R. Filip, “ Laser nitriding of the surface layer of Ti6Al4V titanium
alloy,” Archives of Materials Science and Engineering Volume 30
Issue 1. 2008, Pp. 25-28.
[14] V.Vijay, Arjun, K. Arun, H, K., Vinoth, A. K, Chandrasekar, P. and
Balusmy, V. “ Review of various surface treatment techniques on
titanium alloys and their protective effects against corrosion,”J.
Surface Sci. Technol., Vol. 23, No. 1-2, 2007, Pp. 49-58, Indian
society for surface science and technology, India.
[15] J. M. Kim, S. G Lee, J. S. Park and H. G. Kim, “Laser Surface
Modification of Ti and TiC Coatings on Magnesium Alloy,” ISSN
0031_918X, the Physics of Metals and Metallography, Vol. 115, No.
13, 2014, pp. 1389–1394.
[16] R. Filip, “Alloying of surface layer of the Ti-6Al-4V titanium alloy
through the laser treatment,” Journals of Achievements in Materials
and Manufacturing Engineering. Volume 15, 2006, Issue 1-2.
[17] N. M. Baloyi, A. P. I. Popoola and S. L. Pityana, “laser coating of
zirconium and ZrO2 composites on ti6al4v for biomedical
applications,” South African Journal of Industrial Engineering. Vol.
25 (1), 2014, Pp. 62-70.
[18] O. F. Ochonogor, C. Meacock, S. L. Pityana, P. A. I Popoola,. J. M.
Dutta,” Microstructure characterization of laser-deposited titanium
carbide and zirconium-based titanium metal matrix composites” J. S.
Afr. Inst. Min. Metall. vol.112, 2012 n.10.
[19] H. K. D. H. Bhadeshia, “Martensite and Martensitic Phase
Transformations” www.msm.cam.ac.uk/phase
trans/2002/martensite.html
[20] J. Th. M. De Hosson, C. A. Brebbia, Surface Effect and contact
Mechanics XI. Technology & Engineering.
[21] W. Yan , L. Dai, C. Gui “ In situ synthesis and hardness of
TiC/Ti5Si3 composites on Ti-5Al-2.5Sn substrates by gas
tungsten arc welding” International Journal of Minerals,
Metallurgy, and Materials. 2013, Volume 20, Issue 3, pp 284-289.
Proceedings of the World Congress on Engineering 2016 Vol II WCE 2016, June 29 - July 1, 2016, London, U.K.
ISBN: 978-988-14048-0-0 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
WCE 2016